1. Field of the Invention
This invention relates to silicone elastomer compositions which cure on substrates to self-adhering elastomers and to methods for their preparation.
2. Description of the Prior Art
Adhering to silicone elastomer to substrates is a problem. Attempts to solve the adhesion problem of silicone elastomers has taken many forms. Some solutions have been successful within limits. Additional solutions are still needed. Priming a substrate prior to applying an uncured silicone elastomer composition is one solution. The priming methods are adequate for the purpose of achieving a strong bond, but they suffer from the inconvenience of being at least two step processes. Another solution is the use of one or more additives in compositions to impart the adhesion property between a cured elastomer and a substrate. Additives are usually specific for each composition, application, and condition under which they are used. Most additives have shortcomings, such as interfere with cure or vulcanization of the composition, cause one or more of the cured properties of the product to decrease, are limited to the substrates to which the cured composition will bond, reduce the shelf stability of the composition, and increase the cost of the composition significantly.
U.S. Pat. No. 3,873,334 and U.S. Pat. No. 3,960,800 describe primers for use with silicone elastomer compositions which cure through the reaction of alkenyl groups and silicon-bonded hydrogen atoms. These patents describe applying primers to substrates to achieve adhesion and do not suggest the use of additives to silicone elastomer compositions for the purpose of enhancing the adhesion.
U.S. Pat. No. 3,699,072 describes a composition of a vinyldiorganosiloxy endblocked polydimethylsiloxane and a mixture of an organosiloxane having 5 to 20 silicon atoms per molecule and an average of at least three silicon-bonded hydrogen atoms per molecule and a modified organosiloxane having 6 to 21 silicon atoms per molecule, an average of at least two silicone bonded hydrogen atoms per molecule and an average of at least one unit of EQU (RO).sub.3 Si(CH.sub.2).sub.x CH.sub.3 SiO, (RO).sub.3 Si(CH.sub.2).sub.x (CH.sub.3).sub.2 SiO.sub.0.5
and mixtures thereof where R is methyl, ethyl or acetyl and x is 2 or 3 is curable to an elastomer which has improved unprimed adhesion to substrates, particularly metal substrates.
This reference teaches a composition which cures through the reaction of vinyl groups on silicon with hydrogen atoms on silicon. The modified organosiloxane is part of the crosslinker system which has been modified to include the radicals specified above. The reference does not teach an additive such as that taught by the instant invention.
U.S. Pat. No. 3,892,707 describes silicone elastomer compositions comprising a diorganovinylsilyl-terminated diorganopolysiloxane, or organohydrogen polysiloxane, platinum or platinum compound is the catalyst, and an unsaturated double bond containing isopropenoxysilane, which is represented by the general formula ##STR2## where R is an unsubstituted or substituted monovalent hydrocarbon group, R" is a monovalent organic group having an unsaturated double bond and x is 1, 2, or 3, or a product of its partial hydrolysis-condensation. The compositions are cured on heating with the formation of strong adhesive bonding to the surface of a substrate to which they are in contact.
The isopropenoxysilane of this reference does not teach the usefulness of the amidosiloxane used as an additive to improve adhesion to a substrate as disclosed by the instant invention.